This invention relates to the field of trimmers and in particular to an improved lumber trimmer which may include P.E.T. saws.
As well-documented in the prior art, there is continual development in devices for optimizing lumber production. Typically the optimization of lumber production is accomplished by either increasing the yield rate or the piece rate, or both. That is, optimization of lumber production is accomplished by maximizing the amount of useable lumber obtained from a single raw workpiece such as a log, and this is often optimized to maximize the amount of useable lumber having the highest resale value. As an example of optimising the piece rate, it is desirable to increase the production rate for example by increasing the efficiency of lumber production, often reflected in the maximum maintainable transfer speed expressed in for example feet per minute, lugs per minute or boards per minute. In optimizing the yield rate, speed and accuracy in implementing the optimized cutting solution is important if not paramount.
In the specific instance of a trimming saw or trimmer having multiple saws, where the accuracy of cut may be desirably measured in the tens of thousandths of an inch to optimize the yield rate, and where the piece rates are high for example on infeed conveyors up to 200 lugs per minute, prior art ending of lumber pieces against a fence for example by the use of ending rolls or angled in-line wheels often result in unacceptable inaccuracy due to bounce-back, tip-crush or the like.
In the prior art applicant is aware of U.S. Pat. No. 5,142,955 which issued Sep. 1, 1992 to Hale for a Lumber Cutter for Removing End Defects and Sawing to Desired Lengths. Hale discloses a root end trim saw extending over the root end edge of a lumber piece conveyor. The saw blade is articulated to move down into or up out of the path of lumber pieces and is slidably mounted to be moved over a two-foot range in one-half inch increments to cut away a defective end portion of a lumber piece. The root end trim saw pre-trims a lumber piece which is then ended against a fence prior to entering a trimmer. In use such a saw suffers from at least two drawbacks, namely, that following pre-trimming by the saw the lumber is then ended against a fence reintroducing inaccuracy in positioning of the lumber piece as it enters the trimmer, and, secondly, that at high piece rates the lateral positioning of the root end trim saw within the range specified will limit the transfer rate. The lumber pieces cannot arrive quicker than the time required for the saw to be moved into position for its next cut. As an example, in a worst case scenario, the saw must be translated across the length of its range between the arrival of adjacent lumber pieces. Thus, at high piece rates, it may be required that the conveyor be slowed down until the root end trim saw can be slid into position, thus adversely affecting the optimum piece rate. Consequently it will be appreciated that the design of Hale may adversely affect not only the accuracy of the yield, and thus the yield rate, but also the piece rate.
The optimizer controls obtaining the desired yield from a particular raw lumber piece. In order to do so, the optimizer controls the yield and piece rates. In applicant""s experience, quite often the optimizer optimizes the cutting solution so as to obtain the most-valuable (i.e. highest yield rate) combination of sawn lumber pieces which may be sawn from the raw lumber piece. Where an end trimmer saw, for example the pre-trimmer root end saw of Hale or a so-called precision end trimmer (xe2x80x9cP.E.T.xe2x80x9d) saw is employed, that is, an end trimming saw which is laterally translatable relative to the length of an incoming lumber piece, in a worst case scenario must translate for example 12 inches between adjacent arriving lumber pieces, the optimizer may reduce the infeed conveyor speed (i.e. reduce the piece rate) so as to not adversely affect the yield rate. That is, the optimizer adversely affects the piece rate in order to obtain the highest value yield rate. In applicant""s view, an overall optimized solution in such an instance may be obtained, firstly, by the optimizer implementing for example a second, as opposed to first, most-valuable default cut where the second or lesser valuable default cuts do not, or have a lesser adverse effect on, the piece rate. It is applicant""s view that in the trade-off between a first most-valuable cut and a second or lesser valuable default cut and the trade-off in reducing the piece rate in order to implement the most-valuable cut or maintaining a high piece rate while implementing a second or lesser valuable default cut, a globally optimized result is obtained by maintaining the maximum piece rate and accepting a second or lesser valuable default cut thereby slightly degrading the yield rate. Secondly, rather than merely relying on a single root end or P.E.T. trimming saw, a plurality of root end or P.E.T. saws may be employed.
Use of a plurality such as a pair of P.E.T. saws in conjunction with an active infeed board positioner such as, without intending to be limiting, a live fence or selectively actuable ending rolls or inclined in-line wheels (so called skate wheels), allow for adjacent lumber pieces on the infeed to be end-trimmed, if need be, as for example when two adjacent boards need P.E.T. sawing or a specific (e.g. metric) length is best suited, alternating between for example alternating P.E.T. saws in a pair of such saws. The pair of saws may be opposed facing or may be side-by-side, or may form a subset of a plurality of such saws. Thus, as needed, a first P.E.T. saw may be employed to end-trim a first lumber piece, and a second P.E.T. saw may be employed to end-trim the next adjacent second lumber piece.
The trimmer of the present invention includes a low profile housing which may be accessed for maintenance from the top of the housing by the opening of clam shell doors. The clam shell doors open oppositely so as to pivot about opposite perimeter edges of the top of the housing. The housing defines an upper compartment or cavity which may be closed by closing the clam shell doors. The upper compartment is bisected by a beam, which may be in the form of generally an I-beam. The beam bisects the compartment and runs parallel to perimeter edges about which the clam shell doors pivot.
The vertical webbing of the beam is apertured. The upper flanges of the beam mate with the distal ends of the clam shell doors when the doors are closed. The clam shell doors may be pivoted either manually or with the assistance of actuators known in the art. The floor of the cavity may be sheeted so as to provide a walkway for maintenance personnel. One or more of the clam shell doors may also be sheeted and shaped, so that when fully open, a further walkway is provided along the length of the trimmer housing.
A laterally spaced-apart array of drop saws are mounted along one half of the compartment, that is, on one side of the center beam. The drop saws are rotatably mounted on saw ladders which themselves are pivotally mounted to the beam web. The saw drive motors and the saw ladder actuator are mounted on the opposite side of the beam web, in the other half of the compartment. The actuator may be a cylinder which strokes through an aperture in the beam web so as to drive one end of a bellcrank-shaped saw ladder, the drop saws mounted at the opposite end of the bell crank. The drop saws may be each driven by a pair of drive belts, where the first drive belt extends between the saw hub and the pivoting hub of the saw ladder, and the second drive belt extends from the pivoting hub of the saw ladder to a drive shaft of a drive motor.
In one embodiment of the present invention, a single drive motor drives a pair of first drive belts where each of the pair of first drive belts drive oppositely disposed shafts extending through the pivot hubs of the saw ladders so as to thereby drive a pair of second drive belts, each of the second drive belts driving one of a pair of opposed facing drop saws.
In this arrangement, maintenance personnel merely have to open the clam shell doors and step down into and along the walkway for easy access to a malfunctioning drop saw drive belts or its associated actuator or actuating valves or motor or electronics or the like. Because the pair of second drive belts are most outwardly disposed on either side of the opposed facing pair of drop saws, maintenance tasks are eased by the ease of access to those drive belts. An eccentric surface on the saw ladder pivot tubes, to which the saw ladders are releasably rigidly mounted and which rotate within pivot housings mounted to the web of the beam, provides that releasing the rigid mounting of the saw ladder to the pivot tube allows rotation of the eccentric surface so as to thereby tension or detension the second drive belts. this allows easy removal or replacement of those drive belts. Servicing of the drop saw blades is also facilitated. The arrangement also maintains drive belt tension during pivoting of the saw arbors because the first and second drive belts rotate about a common shaft which is co-axial with the axis of rotation of the saw ladder. Again, because of ease of access, once the clam shell doors are open, into the compartment containing the drop saw drive and actuators, maintenance is thereby eased for those components. The use of a center beam to mount the saw arbors also eases the task of aligning the saws and adjusting the spacing between the saws. In particular, the pivot housings may be releasably mountable to the beam web, for example into a preformed or machined mating channel, so that the pivot housings may be adjusted relative to the length of the beam and secured thereto once desired spacing has been achieved. The clamping of the pivot housing to the beam web once the desired spacing has been achieved, thereby assists in attaining the alignment of the saws.
In summary then, in one aspect of the present invention a lumber trimming device is provided for trimming elongate workpieces conveyed on an infeed conveyor in a laterally disposed orientation relative to an infeed direction of the conveyor. The lumber trimming device operates in cooperation with an optimizer, and includes a gang of laterally spaced apart drop saws. The drop saws are independently actuable by actuating means according to trimming instructions from the optimizer. An end-trimming saw is mounted adjacent the gang. The end-trimming saw is selectively laterally translatable and in the preferred embodiment is only laterally translatable, that is, is not a drop saw or otherwise elevatable. Lateral translation is by selectively actuable translation means according to end-trimming instructions from the optimizer. The end-trimming saw thereby cooperates with the gang.
The end-trimming saw cooperates with the optimizer and the drop saws so that a first drop saw of the drop saws is actuated simultaneously with optimized lateral positioning of the end-trimming saw. Thus a first workpiece of the workpieces on the infeed conveyor is trimmed simultaneously by both the first drop saw in a first trim cut and the end-trimming saw in a second trim cut.
The end-trimming saw may be a first end-trimming saw which cooperates with the translation means and the optimizer to laterally re-position the first end-trimming saw subsequent to the second trim cut simultaneously with a second end-trimming saw mounted adjacent the gang actively laterally pre-positioning for an end trim cut on a second and next-adjacent workpiece on the infeed conveyor. The second end-trimming saw may, again, be only selectively laterally translatable the second end-trimming saw is translated by second translation means.
The second end-trimming saw may be mounted adjacent the first end-trimming saw. The first and second end-trimming saws may be mounted on a first side of, or in opposed facing relation on either side of, an infeed flow path of the workpieces passing into and through the gang. In the first instance the first and second end-trimming saws are in parallel alignment for parallel lateral translation during the lateral translation of the first and second end-trimming saws. In this embodiment the second end-trimming saw may be downstream of the gang and the first end-trimming saw may be generally laterally aligned with the drop saws. In the second instance, the first and second end-trimming saws are aligned for co-axial lateral translation during the lateral translation of the first and second end-trimming saws, and thus the first and second end-trimming saws are generally laterally aligned with the drop saws.
A further aspect of the invention includes workpiece clamping means for clamping a workpiece passing through the gang and downstream to the second end-trimming saw so as to prevent movement of the workpiece during the end trim by the second end-trimming saw.
The end trimming saws cooperate with the optimizer to default to lateral positions at a sub-optimal yield solution rather than positions for a trim solution optimized for yield if an optimized piece rate of the infeed must be reduced in order to effect said trim solution optimized for yield.